Cellulosic textiles are commonly dyed with a mixture of vat and disperse dyes on a commercial scale using a continuous dyeing process known as the Thermosol process. The Thermosol process is described in the U.S. Pat. No. 3,957,427 to Chambers, which is incorporated herein by reference. This process may be characterized as having the following five steps (1) passing a cellulosic textile through a pigment pad containing a mixture of an unreduced vat dye and a disperse dye; (2) drying the dye-impregnated textile; (3) fixing the disperse dye on the dry textile by a heat treatment operation; (4) passing the textile with the unreduced vat dye and fixed disperse dye thereon through an alkaline reducing solution, called the chemical pad, at a temperature, below the vat dye reduction temperature, e.g. about 70.degree. F. to 90.degree. F., and (5) passing the textile with the dyes and reducing solution thereon into an air free developing chamber. In the developing chamber, the textile is subjected to steam.
It has been known that dye particles tend to migrate during the intermediate drying step of the aforementioned continuous dyeing process. The dye migration, which is uncontrolled and random in nature, leads to uneven dyeing which results in variations in the shade of the final dyed product. Such shade variation can detract from the appearance of the textile such as extent that the final dyed product is unmarketable.
In the past, various antimigrating agents have been added to the pigment pad in order to minimize dye migration. Among the agents disclosed in the prior art are natural gums, sodium alginate, and amide derivatives of polyvinyl methyl ether/maleic anhydride mentioned in the 3,957,427 patent and sodium chloride, Kelgin RL (Kelco Co.) and Superclear 100N (Diamond Shamrock) mentioned in Textile Chemist and Colorist, 7, 192 (1975); both of these are incorporated herein by reference.
None of the various antimigrating agents described in the prior art has found universal acceptance in the textile dyeing industry. Many agents merely increase the viscosity of the dye dispersion in the pigment pad without controlling migration significantly. Some agents tend to coagulate dye particles and consequently reduce color yield. Furthermore, the additional cost of certain antimigrating agents had discouraged their use on a commercial scale.